1. Field of the Invention
The present invention relates to a linear guideway, and more particularly to a rolling element chain system for a linear guideway, which can avoid the occurrence of interference, can create radial freedom and can effectively avoiding the falling-off of the rolling elements and can further make every rolling element share the load evenly.
2. Description of the Prior Art
Nowadays, linear guiding devices are applied in the industry more and more, besides the high precision effect for the linear feed transmission, it further has the advantages of low frictional loss ratio, high energy-conversion ratio, low noise, and high rigidity not easy to damage etc. Hence, it is self-evident that the linear guideway is very important to the existing various industrial mechanisms. A common linear guiding device is a linear guideway consisting of a slide block, a slide rail and rolling elements interposed between the slide block and the slide rail, and the rolling elements linearly move and rotate within the track defined by the slide block and the slide rail, but the rolling elements are placed into a rolling element chain one by one and are retained and separated by the chain in order to achieve the following objectives:
1. preventing the rolling elements from falling off the slide block when the slide block disengages from the slide rail;
2. avoiding increase of frictional force caused by mutual contact of the rolling elements; and
3. enabling the rolling elements to be positioned regularly to achieve the smooth movement.
The common conventional rolling element chains include two types of chains, one is end-type and the other is endless-type.
The rolling element chains disclosed in JP Pat. No. 3243415, as shown in FIG. 1 and JP Pat. No. 3263005, as shown in FIG. 2 are both end-type. In JP Pat. No. 3243415, there is a clearance between the two ends of the chain 10. In JP Pat. No. 3263005, a rolling element 101A is placed between the two ends 11A of the chain 10A, but there is still a clearance 12A between the two ends 11A and the rolling element 10A. The above two conventional chains will have the following disadvantages due to the influence of the clearance.
The disadvantages of the conventional chain disclosed in JP Pat. No. 3243415 are described as follows.
1. The two ends of the chain 10 are free due to the clearance therebetween, so the chain is likely to sway during use, or even worse, the two ends 11 might impact or cause frictional interference with the return path when passing through it;
2. In addition, when passing through the return path, since the two ends 11 of the chain 10 are disconnected from each other, the two ends 11 will shift toward the outer edge of the return path in such a manner that the two sides of each of the rolling elements 12 neighboring to the two ends 11 are not symmetrical, causing the discontinuous unsmooth operation of the linear device, and the smoothness of the operation is further worsened when the two ends 11 impact or interfere with the return path.
Regarding the JP Pat. No 3263005: the rolling element 101A between the both ends 11A can prevent the ends 11A of the chain 10A from shifting toward the outer edge of the return path, ensuring a smooth operation. In order to avoid excessive justle caused by the fact that the chain 10A might be lengthened after a long time of use, the clearance is left between the rolling element 101A and the two ends 11A, however, the problem is that the rolling elements 101A are not evenly distributed, furthermore, the rolling element 101A is not confined and likely to fall off the rail.
In order to overcome the above problems, devices, such as are disclosed in JP Pat. Publication No. 11-294452, as shown in FIG. 3 and JP Pat. No. 2607993 as shown in FIG. 4, are developed on the market. In JP Pat. Publication No. 11-294452, the rolling element chain 14 is an endless chain with both ends 15, 16 engaged with each other. In JP Pat. No. 2607993, the chain 17 is integrally formed as an endless structure, and the rolling elements 18 are retained in the chain 17 respectively. The above two conventional chains can avoid the previous impact problem, but they still have the following problems to be improved.
The above conventional chain 14 or chain 17 is likely to cause shortening stress and stretching stress continuously with collision of the rolling elements, and these designs are unable to reserve extension space for the chain 14 or the chain 17, so there is no radial freedom for absorbing the entire length variation of the chain, still causing the unsmooth movement.
This problem is more obvious in JP Pat. No. 2607993, although every rolling element 18 can share the load evenly, the radial size variation cannot be absorbed. On the other hand, when it needs to readjust the pre-load, the number of the rolling elements 18 must be adjusted. However, since the chain 17 is integrally formed, the number of the rolling elements 18 is fixed and unchangeable since it has to break the chain 17 if want to add or remove rolling elements 18.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.